Atmospheric scientists to weather the stormiest place on Earth

The answer was a sparse region in Argentina’s Andean foothills. Rasmussen, then a University of Washington graduate student, flung herself into studying the monstrous storms that darken subtropical South American skies: their structure, their genesis, and why they occur there, and not elsewhere.

Now a Colorado State University assistant professor in the Department of Atmospheric Science, Rasmussen will finally get to stand under those very skies, putting her hypotheses to the test.

Rasmussen is a key contributor to a $30 million, National Science Foundation-funded field campaign, launching Nov. 1, aimed at discovering why thunderstorms in this particular region of Argentina are among the most extreme in the world. The scientists will help improve the knowledge and prediction of violent storms in this part of the world, as well as for severe weather in general.

“It’s very exciting,” Rasmussen said. “I have studied these storms for over 10 years, but never seen one in person. I’m thrilled to go down to the field with great colleagues and instruments, and sample some of the most extreme thunderstorms on Earth.”

Cooperative effort

The six-week scientific campaign is called RELAMPAGO (Remote sensing of Electrification, Lightning And Mesoscale/microscale Processes with Adaptive Ground Observations), which translates to “lightning” in Spanish and Portuguese. It involves about 160 researchers and students from CSU, University of Illinois, University of Washington, University of Utah and Penn State, as well as the Department of Energy, the National Center for Atmospheric Research, and international partners. The project is also funded by the National Oceanic and Atmospheric Administration (NOAA), NASA, and other federal and provincial agencies in South America.

Advanced Study Institute for U.S. grad students

In addition to her fieldwork during RELAMPAGO, Kristen Rasmussen will lead an NSF-funded Advanced Study Institute: Field Studies of Convection in Argentina program for 16 U.S. graduate students from diverse backgrounds without prior field campaign experience, including CSU students Jeremiah Piersante and Alexandra Naegele. The students will gain experience in the planning and execution of a large, complex field experiment, and learn from all the RELAMPAGO scientists as they work. These students will be paired with an Argentine and Brazilian cohort to enable international networking opportunities and meaningful career-defining experiences.

A complementary, Department of Energy-supported campaign called CACTI (Clouds, Aerosols and Complex Terrain Interactions) will take place at the same time. Together, RELAMPAGO and CACTI will make up the largest land-based atmospheric sciences field campaign ever conducted outside the U.S.

“The frequency and intensity of rainfall in South America makes the region an ideal natural laboratory to increase our understanding of heavy rain-producing storms around the globe,” said Chungu Lu, a program director in the NSF Division of Atmospheric and Geospace Sciences, which funded the project.

According to RELAMPAGO lead researcher Steve Nesbitt of the University of Illinois (who completed a postdoc at CSU), the region they’re studying is unique for its topography, with the Pampas lowlands and the Andes mountains in close proximity. The terrain provides the ideal situation for the formation of storms that impact a wide region of South America.

“Argentina turns out to be a very special place,” Nesbitt said. “The severe storms are similar in some ways to the U.S. Great Plains, where we experience severe thunderstorms, but the geography is quite a bit different, which may have important controls on how thunderstorms behave. It may be that Argentina sets the stage for thunderstorms which we think are the strongest on Earth.”

CSU expertise

During the campaign, Rasmussen and her graduate students will work primarily with a network of C-Band and X-Band radars, using real-time algorithms for processing data as storms develop. They’ll make on-the-fly decisions on where and how the radars should scan, sampling as many storms as possible from start to finish.

Joining Rasmussen and her students from CSU will be groups led by Russ Schumacher, associate professor in the Department of Atmospheric Science, and V. “Chandra” Chandrasekar, University Distinguished Professor in the Department of Electrical and Computer Engineering and Cooperative Institute for Research in the Atmosphere. Among the deployed scientific instruments will be a C-Band radar from Chandrasekar’s laboratory.

“Our scientific goals are ultimately to better understand the types of storms that produce heavy precipitation, and the processes that lead to that,” said Schumacher, who is also the Colorado State Climatologist. “We anticipate that we will observe things we have never observed before.”

Over several weeks, Schumacher’s group will launch about 100 mobile radiosondes, using weather balloons, to track the progression of storms. They will also contribute to the forecasting team for RELAMPAGO, helping to choose which days to go out and collect data.

Tall, lingering storms

The scientists are traveling to a region about 30 miles west of Cordoba, Argentina, which abuts the foothills of the Andes mountain range. The region lacks the level of coverage from radar networks and other weather prediction infrastructure that the U.S. has.

Previous research by Rasmussen and others has found that storms in this territory initiate near the mountains and tend to linger, growing extremely high, producing heavy precipitation and sometimes golf-ball or grapefruit-sized hail. Storm genesis is similar in the Rocky Mountains, but in the Rockies, storms tend to move off quickly, not growing as tall and intense. Rasmussen’s team is looking to verify whether the average 50-percent higher elevations of the Andes contributes to slow progression of storm activity and subsequent deepening in the atmosphere.

The field campaign will deploy a vast array of instrumentation. To intercept storms from their formation through maturity, mobile instrumentation will hone in closely and observe the internal structures of storms. Networks of fixed and mobile radars, including the famous “Doppler on Wheels,” will profile the storms to observe the production of heavy rainfall, strong winds and hail.

Environments around storms, thought to be important in dictating how storms develop, will be observed with rapid-fire weather balloon launches led by Schumacher’s team; mobile weather stations; and instrumented vehicles that capture small-scale weather patterns. An instrumented aircraft will observe conditions aloft within very early stages of developing storms, and surrounding them once they become too dangerous to fly near.

Continuous three-dimensional lightning instrumentation will allow examination of storm characteristics and electrification together, to improve understanding of why Argentine storms produce copious lightning. As the intense precipitation falls on land, a “flood-chasing” team will measure streamflow in the rivers. Drones, local citizens’ mobile phone apps and hail pads, originating from CSU’s CoCoRaHS program, will help monitor hail fall.

Despite a team of expert forecasters, the campaign involves many safety precautions to ensure the scientists can take cover should a massive storm overtake them, and to preserve their sensitive equipment. Remember the possibility of grapefruit-sized hail?

“We will have bike helmets and things like that to make sure we are protected,” Rasmussen said